Immunohistochemical identification of somatostatin-containing neurons projecting to the median eminence of the rat.

Immunohistochemical staining of somatostatin (SRIF) and a retrograde transport method with horseradish peroxidase (HRP) were simultaneously applied to the same section of the rat brain to identify the specific SRIF-containing neurons sending their fibers to the median eminence. After HRP injection into the median eminence, SRIF-positive neurons in the rostral parts of the periventricular nucleus were shown to be labeled with HRP, SRIF neurons in the other brain areas, such as the amygdala, the ventromedial nucleus, dorsomedial nucleus and arcuate nucleus, had no HRP-positive material. The present findings appear to demonstrate that SRIF neurons in the periventricular nucleus project directly to the median eminence.